The art of plastic molding and particularly injection molding has developed to a point of considerable sophistication. With improved technology, plastics have been developed with a wide variety of physical and chemical properties. Resins and molding compounds are available or may be modified to provide plastics which are rigid or flexible, brittle or impact resistant, soluble or resistant to solvents, clear or opaque, dense or expanded, etc. For any particular application, an expert in the art of plastic technology may select and/or tailor a resin or molding compound to the needs of the application.
It has been known to mold an article in which sections thereof are differently colored. Portions of the resin melt are isolated and color dyes are introduced therein prior to introduction into the mold. Alternatively, different color dyes have been introduced into the resin, per se. The isolated melt portions differ only to the extent that they are of different colors and the cured article produced therefrom is multicolored. The properties of the cured article are, however, substantially uniform throughout. A two-color sign or a typewriter key are typical examples. According to this known process, the differently colored melt portions must be separated along a sharply defined interface after introduction into the mold to avoid blurring and for sharp letter definition. To produce articles using a differently colored resin, one known technique is to first inject one colored melt portion into a mold and, after it cools and sets, inject the other differently colored melt portion therein so that the materials will be maintained separate, one from another. According to another known technique, the differently colored melt portions are simultaneously injected into the mold. Both known processes have as their end product an article with substantially uniform properties, except as the properties thereof may vary according to thickness variations therein. Neither known process provides an article with one or more selectively localized areas having preselected property characteristics which differ from characteristics of the main body of the article; nor do these known processes provide an article with a transition zone of intermediate characteristics between the localized area and the main body thereof.